Home Forums Shifter Karts TM tuning issue

This topic contains 10 replies, has 4 voices, and was last updated by  Matt Martin 2 days, 4 hours ago.

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    Brad Clem

    I recently acquired a kart with a K9B after running a CR125 for a couple of years.  I keep getting the same running problem no matter jetting changes, float adjustment, plug gaps (just for testing), fuel pumps, lines, etc.

    So the problem comes up when I exit a long sweeping turn after a WOT section.  I hold the throttle about 50% through the turn, then return to WOT and it spits and sputters until I get slow enough, then it dies.  When I look at the fuel feed line to the carb, it is empty.

    The kart came with 2 Dellorto carbs.  Both act the same, so I put the Keihin from the Honda on it.  Same problem, but seems to need a sharper turn to develop.

    Yes, the gas tank is full.

    Any help would be appreciated.



    • This topic was modified 3 days, 19 hours ago by  Brad Clem.

    Glenn L Riggs

    Check pick up tube in tank and tank vent.


    Brad Clem

    Confirmed pickup tube is clear, no cracks in the line.  Vent is open.


    Matt Martin

    Has to be a fuel pick-up issue if it’s happening with three carbs.


    Fuel pick up system:

    – Pulse fitting (could be affected by reeds, or crank-case sealing)

    – fuel pump

    – feed/pick-up line

    – Pump-to-carb/return line.

    Have you restricted the fuel-pump return hose with a zip tie or clamp?


    can you post a photo of the fuel line circuit?

    Does the problem occur on left and right sweepers?



    Makes a lot of sense, I agree with the guys.

    I have a strong feeling it’s your pick up hose in the tank, even though it may look good, you may have a crack right at the top above fuel level, near the fitting, and when you turn on sweeper the “G” force the bottom pick up sideways and it opens up the crack up on top, causing the system to only suck air.

    Remove complete pick up set up out of the tank, remove bottom piece or block it, the slightly blow some compressed air through the top fitting, spray some soap or just feel for air leakage. I hope this does it for you. Good luck.


    Brad Clem

    – Pump-to-carb/return line.

    Pulse line and feed line (pump to carb) are new.

    Pulse fitting appears to be ok.

    2 sets of reeds and cages have been in it.

    Fuel pump is new.

    No static restriction.  No apparent dynamic restriction.

    Left or right, it does not discriminate.

    Output fuel line had a Y that fed carb and return, while blocking the other port at the pump.  I put a new pump on and re-routed pickup in, return out, carb out.

    The pickup tube was hardened and would not come off either end.  I just now put the one from the Honda on it (replace with known good) and will test at an autocross on Sunday.
    Thanks for all the replys.



    Matt Martin

    This is how I have mine routed, and have not run into this issue (I also have a slight restriction in the return line):


    TM K9 Fuel routing


    Brad Clem

    IMG_0638That’s a coupler at the bottom of the picture

    • This reply was modified 2 days, 5 hours ago by  Brad Clem.

    Matt Martin

    In addition to making sure there are no cracks in the tank’s pick up line (and/or bulkhead), I would suggest using a Y or a T to connect the both pump outlets to a single hose, then another Y to branch them back out.  One returning to the tank – with a restriction – and one feeding the carb.

    The only other thing I can recommended is if you have any in-line filters, to make sure they are tight, and not able to introduce air into the system under any kind of loading.





    Brad Clem

    I see that you are maximizing volume on the carb side of the pump.  I will reroute as you suggest.  I have a filter on the feed line to the pump.  Would this cause a loss of pressure?  Should I move it to the return line to increase fuel pressure fed to the carb?  Then change the carb screen more often.


    Matt Martin

    I would suggest the filter be on the feed line from the tank to the pump.

    My only suggestion there is to inspect the filter and see if it is faulty and could potentially introduce air.  Try to flex it and see if there’s any give which could open a gap – I suspect that’s quite unlikely.

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